Hi frugalri,
I would do some significant research on this vendor and the accuracy of their listings before making a purchase from them (see post #2 here).
I would also make very sure that the listed specs are accurate (your google research will bring up more information about this), ask them some very specific questions about how they calculate foam densities, and confirm the shipping weight both before and after a purchase although if it’s after a purchase then it would probably be too costly to return the mattress if they were incorrect.
I would be VERY cautious here.
Phoenix